Send a digitally signed or encrypted message

A digital signature on an e-mail message helps the recipient verify that you are the authentic sender and not an impostor. Encryption of a message scrambles the message text so that only your intended recipients can read it.

To use digital signatures and encryption, both the sender and recipient must have a mail application that supports the S/MIME standard. Outlook supports the S/MIME standard.

Send a digitally signed message

Before you start this procedure, you must have added a certificate to the keychain on your computer. For information about how to request a digital certificate from a certification authority, see Mac Help.

  1. On the Tools menu, click Accounts.

    Accounts button on the Tools tab

  2. Click the account that you want to send a digitally signed message from, and select Advanced > Security.

  3. In Certificate, select the certificate that you want to use. You'll only see those certificates that you've added to the keychain for your Mac OS X user account and that are valid for digital signing or encryption are listed here. To learn more about how to add certificates to a keychain, see Mac Help.

  4. Do any of the following:

    To make sure that your digitally signed messages can be opened by all recipients, even if they do not have an S/MIME mail application and can't verify the certificate, select Send digitally signed messages as clear text.

    To allow your recipients to send encrypted messages to you, make sure that you've selected your signing and encryption certificates, and then select Include my certificates in signed messages.

  5. Click OK, and then close the Accounts dialog box.

  6. In an e-mail message, select Options > Security > Digitally Sign Message.

    Security and permissions buttons in Outlook 2016

  7. Finish composing your message, and then click Send.

Send an encrypted message

Before you start this procedure, you must first have a certificate added to the keychain on your computer. For information about how to request a digital certificate from a certification authority, see Mac Help. You must also have a copy of each recipient's certificate saved with the contacts' entries in Outlook. For information about how to add your contacts' certificates to Outlook, see Import, export, or remove a certificate for a contact.

If your recipient is listed on an LDAP directory service, such as the global address list (GAL) with Microsoft Exchange Server, the recipient's certificate is published to the directory service and available to you together with other contact information.

If your recipient is listed on an LDAP directory service, the recipient's certificate is published to the directory service and available to you together with other contact information.

  1. On the Tools menu, click Accounts.

    Accounts button on the Tools tab

  2. Click the account that you want to send an encrypted message from, and select Advanced > Security.

  3. In Certificate, select the certificate that you want to use. You'll only see those certificates that you've added to the keychain for your Mac OS X user account and that are valid for digital signing or encryption are listed here. To learn more about how to add certificates to a keychain, see Mac Help.

  4. Click OK, and then close the Accounts dialog box.

  5. In an e-mail message, select Options > Security > Encrypt Message.

    Security and permissions buttons in Outlook 2016

  6. Finish composing your message, and then click Send.

    Note: When you send an encrypted message, your recipient's certificate is used to encrypt his or her copy of the message. Your certificate is used to encrypt the copy that is saved to your Sent Items or Drafts folder in Outlook.

See Also

Secure messages by using a digital signature in Outlook for PC

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